Category Archives: Exhausts & Emissions

Diagnosing a Failed Lambda Sensor

Diagnosing a Failed Lambda Sensor

First fitted to passenger cars in the 1970s to improve the engine’s combustion efficiency and reduce exhaust emissions, the lambda sensor is now a key component within the engine management system. But what are the visual symptoms of failure?

In order to operate efficiently, an internal combustion engine requires the correct ratio of air and fuel in its cylinders during the combustion process, with the ideal – known as lambda – being 14.7 parts air to one part fuel for a petrol engine and 14.5:1 for a diesel. Lambda sensors operate by measuring the amount of oxygen in the exhaust, to allow the engine management system to make the necessary adjustments to remain as close as possible to the ideal ratio.

These measurements have now become so precise that many vehicles feature several lambda sensors situated in the exhaust system, both before and after the catalytic converter. As global emissions standards have become ever more stringent, the variety and complexity of lambda sensors has increased accordingly and now includes zirconia, titanium, planar and wideband.

Causes of failure

The lifespan tends to be 45,000 miles for an unheated sensor, whereas a heated sensor can typically last closer to 100,000 miles, so many will simply fail due to age. However, vibration or damage to the heater element, connectors and/or wires could be a cause of premature failure. Other less obvious reasons can be identified by examining the visual appearance of the failed sensor.

A guide to visual symptoms and possible causes

ANTIFREEZE CONTAMINATION

Visual signs – The sensor nose will have a grainy white/light grey coating.

The cause – Coolant with anti-freeze may have affected the combustion process and reached the lambda sensor.

The solution – Check the head gasket for leaks and repair if required.

ENGINE ADDITIVE CONTAMINATION

Visual signs – The sensor nose will be contaminated with white or red deposits.

The cause – Excessive use of an engine or fuel additive can contaminate or block the lambda sensor.

The solution – Cleaning the fuel system prior to replacement.

OIL CONTAMINATION

Visual signs – Oily black deposits left on the sensor nose.

The cause – The vehicle may be burning excessive oil.

The solution – Prior to sensor replacement, thoroughly check the engine for leaks, including the usual seals that are prone to failure.

FUEL CONTAMINATION

Visual signs – Black soot on the sensor nose.

The cause – A damaged sensor or fault in the fuel system can result in a high air to fuel ratio, producing black soot.

The solution – Measure exhaust gases to ensure the fuel system is working. Check the sensor heater control and sensor heater.

LEAD CONTAMINATION

Visual signs – The sensor nose is contaminated with shiny grey deposits.

The cause – Now far less common, but usually caused by leaded fuel attacking platinum parts or the sensor.

The solution – Replace any leaded fuel in the system before fitting the replacement sensor.

Catalytic Converter Analysis with Bosch FSA

Catalytic Converter Analysis with Bosch FSA

This video demonstrates the Catalytic Converter Analysis with Bosch FSA

The EU emission standards – Tech Talk from Comma Oil

What are the EURO emission standards?

The EURO emission standards define the acceptable levels for exhaust emissions of new vehicles sold in EU member states. These standards are generally accepted to be the single most important driver to technology changes in the automotive industry. Currently, emissions of nitrogen oxides (NOx), total hydrocarbons (THC), non-methane hydrocarbons (NMHC), carbon monoxide (CO) and particulate matter (PM) are regulated for most vehicle types, including passenger and commercial vehicles. For each vehicle type different standards apply.

What’s the current standard?

EURO I was introduced in 1993 and since then increasingly demanding standards have been progressively released. We are currently at Euro 6 which when compared to EURO 3 has resulted in around a 90% reduction in the key categories for diesel engines and
about a 60% reduction in the key areas for petrol engines. Euro 6 present some substantial challenges particularly for diesel engines
in commercial vehicles as well as passenger vehicles. This has significant implications for emissions control technologies, requiring the integration of emission control aftertreatment for Particulates (PM), such as DPFs (Diesel Particulate Filters) and NOx emissions, such as CATs (Catalytic Converters) and SCRs (Selective Catalytic Reduction with AdBlue).

Screen Shot 2017-05-04 at 12.08.38

What are the consequences of the increasingly demanding EURO standards?

Tougher regulations are forcing manufacturers to continuously improve the fuel economy of their engines, to produce less oil waste and, most importantly, to reduce emissions across their vehicle range. The EURO emission standards are the main driver for automotive technology for both passenger and commercial vehicles. To meet these increasingly demanding regulations, manufacturers are having to improve their engines by introducing new components like EGR (Exhaust Gas Recirculation) valves, turbochargers and exhaust after treatment systems. These changes result in much more complicated and variable engine configurations which in turn can lead to quite different requirements for engine oil.

Turbochargers are nowadays quite common on both diesel and petrol passenger vehicles, why is this?Screen Shot 2017-05-04 at 12.13.27

That’s simply because of the benefits they bring when it comes to meeting those challenging environmental regulations. All diesel cars manufactured today are turbocharged and according to statistics provided by BTN turbo, around 30% of petrol vehicles were fitted with a turbocharger by the end of 2012 and overall 70% of the market will be turbocharged by 2020.

However, turbochargers present some unique challenges when it comes to lubrication because of the extreme conditions under which they operate. According to turbocharger experts BTN Turbo, 95% of turbocharger failure is caused by a lubrication fault of some kind.

Can engine oil contribute to catalytic converter (CAT) or diesel particulate filter (DPF) damage?Screen Shot 2017-05-04 at 12.13.53

Exhaust after treatment systems like DPFs or CATs are very sensitive and expensive components that can be damaged if the right Low SAPS (Low Sulphated Ash, Phosphorus and Sulphur) oil is not used. SCR systems can also be damaged by excessive levels of Phosphorous.

Screen Shot 2017-05-04 at 12.10.45

Exhaust gas recirculation system (EGR)

Screen Shot 2017-04-27 at 14.35.50General

To achieve exhaust emission reductions, some vehicles, are fitted with an exhaust gas recirculation system. This system is controlled by the ECU and the EGR valve.

Function

Due to the recirculation of a part of the exhaust gas the NOx concentration can be reduced. The recirculated exhaust gas, supplied to the air intake, will not combust, it absorbs a part of the combustion heat and warms up. This causes a drop in the combustion temperature. A lower combustion temperature causes a lower NOx concentration. To ensure that always the right quantity is recirculated the control follows the engine performance maps of the ECU. There are two control possibilities: The direct connection between the ECU and the EGR valve or via a switching valve. In this case, the ECU controls the switching valve that open and close a vacuum line. The vacuum then opens and closes the EGR valve.

Causes of failure

A faulty exhaust recirculation system can produce the following fault symptoms:

  • Engine control light illumination, storing a fault code
  • Black smoke (diesel engine)
  • Rough idling

Causes for a faulty exhaust recirculation system:

  • EGR valve plugged or permanently open
  • Missing control of the ECU / ground
  • Faulty, plugged lines
  • Faulty, plugged vacuum lines
  • Faulty switching valve
  • Faulty wires, bad contact of the connectors

Fault diagnosis

For the fault recognition consider the following steps:

  • Visual check of all relevant components for damage
  • Check of all lines and connectors for damage, correct fitting and size
  • Read out the fault memory (if possible)
  • Check the EGR valve and lines for clogging and fouling
  • Check for supply voltage from the ECU at the switching valve and/or at the EGR valve

Air Flow Sensor (MAF)

General

Screen Shot 2017-04-25 at 14.45.07The air flow sensor records the incoming air flow. It is constructed of a duct style housing with a flow rectifier, sensor protection and a sensor module. The air flow sensor is fitted into the inlet pipe between the air filter housing and inlet manifold.

Function

Two metal film resistors, fitted on a glass membrane, situated in the air flow. The first resistor(RT) is a temperature sensor and measures the air temperature. The second resistor(RS) measures the air flow. Depending on air mass drawn into the resistor RS is cooled down. To compensate for the constant temperature difference between the resistors RT and RS the current flow through the resistor RS must be regulated. This heating current is the measured variable of the air flow drawn in by the engine. This measurement is needed by the ECU to assist in calculating the fuel injection.

Effects of failure

A faulty air flow sensor can cause the following:

  • engine stalls or the ECU switches to limp mode
  • engine warning light illumination

Causes of failure:

  • bad connection at the plug
  • damaged measuring elements
  • mechanical damaged(vibrations, accident)
  • range drift of the measurement elements(wrong scope pattern)

Diagnostics

For fault recognition consider the following system tests:

  1. Check electrical lead for correct fitting and contact
  2. Check air flow sensor for damage
  3. Check measurement elements for damage
  4. Measurement of the operation voltage, ignition on (wiring diagram needed for pin definition), measured value: 7.5 14 V
  5. Measurement of the output voltage, engine runs(wiring diagram needed for pin definition), measured value: 0 . 5 V
  6. Check the wiring harness between the sensor plug and the removed ECU plug for short circuit to earth and continuity, measurement with an ohmmeter between sensor plug and vehicle ground, measured value: >30 Mohm, measurement between sensor and ECU plug, measured value: < 1 ohm
  7. Electronic check of the air flow sensor by the ECU. If there is a failure the ECU stores a fault/trouble code and the engine warning light is illuminated. The fault/trouble code can be read out with a code reader or a diagnostic test equipment.

Sensors and actuators in the induction system – faults and their effect

 

1. Mass air flow meter

General points

The mass air flow meter has the task of determining the air mass supplied to the engine. It comprises a tube-shaped housing with flow rectifier, sensor protection and sensor module screwed to the outside. It is mounted between the air filter housing and the throttle blade.

Effects of failure

A failed mass air flow meter can become noticeable as follows:

  •  The engine stops or the engine management control unitstarts to work in emergency running mode
  •  Loss of power
  •  Engine warning light comes on

Reasons for failure of the mass air flow meter can be

  •  Contact fault at the electrical connections
  •  Damaged measuring elements
  •  Mechanical damage (vibration, accident)
  •  Detachment of measuring elements(leaving the measuring framework)

Troubleshooting

  •  Read out faults stored in the engine management control unit
  •  Visual inspection of the plug-type connection, the cabling,the housing and sensor element
  •  Check the supply voltages and output signals using amultimeter or oscilloscope

2. Throttle blade

General points

Throttle blades are installed between the induction bridge and load sensor. Throttle blades control the air flow sucked in by the engine. The mixing ratio of fuel and air is changed by the throttle blade’s opening angle.

A distinction is made between the following throttle blade parts
1. Mechanical throttle blades

Actuated through the accelerator pedal via rods or Bowden cable

2. Electromotive throttle blades

Triggered through Bowden cable and control unit

3. Electronic throttle blades

Regulated and controlled through the control unit

Effects of failure

  • Loss of power
  • Misfiring during acceleration
  • Vehicle goes into emergency running mode Fluctuating idling speed
  • Engine warning light comes on

Causes of failure are

  • Soiling through oil carbon deposits
  • Mechanical blockage through foreign particles Defective actuator motor
  • Defective potentiometer

Troubleshooting

  •  Read out fault store
  •  Check the supply voltages and signals using amultimeter and oscilloscope
  •  Visual inspection of the cabling and mechanical assemblies

3. Induction pipe pressure sensor

General points

The induction pipe pressure sensor has the task of measuring the negative pressure in the induction pipe, downstream from the throttle blade. Induction pipe pressure sensors can be connected directly to the induction pipe by a hose or be installed directly in the induction pipe.

Effects of failure

A fault in the induction pipe pressure sensor can become noticeable as follows:

  • Great loss of power
  • Misfiring during acceleration
  • Fluctuating idling speed
  • Engine warning light comes on

Typical causes of failure are

  •  Damaged measuring elements
  •  Internal short-circuits
  •  No supply voltage, earth connection
  •  Soiled vacuum connection, torn or damaged vacuum pipe

Troubleshooting

  •  Check sensor for damage
  •  Read out fault store
  • Check vacuum connection, connection plug and cabling

 

 

Lambda sensor

General

Due to the increasing strictness of exhaust emission regulations, the vehicle manufacturers are commited to reducing their vehicle emissions. For this reason a 3-way catalytic converter is fitted to nearly all vehicles. To achieve a good conversion rate from the converter and optimal engine conditions, the fuel-air mixture must be monitored and adjusted. This is the function of the lambda sensor and the ECU.

Function

Screen Shot 2017-04-20 at 14.47.30To get an optimal complete combustion the fuel-air mixture must have a ratio of 1:14,5. This proportion is called λ (lambda) = 1 (fig. 1). To ensure for the best proportion, the lambda sensor measures the residual oxygen content in the exhaust. Dependent on the residual oxygen content a lean or rich mixture is indicated to the ECU by a voltage. The ECU controls, using this measured parameter, the optimal fuel-air mixture. The measurement of the residual oxygen content can b obtained using two different types of lambda sensor: Zirconiumdioxide and Titaniumdioxide . The difference between these two sensors is that the zirconiumdioxide sensor generates a voltage and the titaniumdioxide sensor needs a supply voltage. The construction and function can be explained as following:

Zirconiumdioxide sensor: The zirconiumdioxid eelement has direct contact to the
exhaust gas, protected with a protection sleeve. The inside is exposed to ambient air.

Screen Shot 2017-04-20 at 14.47.41Both sides are coated with a platinum deposit acting as an electrode. Oxygen ions pass over this platinum deposit and leave a voltage. At a temperature of 300 C the zirconiumdioxide element is conductive. If the oxygen content of the out- and inside is
different, a voltage is created due to the elements property. This voltage is the measured variable for the ECU. If the voltage is high the mixture is rich, if the voltage is low the mixture is lean.

Titaniumdioxide sensor: The titaniumdioxide sensor does not generate a voltage. It works using a changing resistance. The changing of the resudial oxygen content also changes the resistance of the titaniumdioxide element. If the element is supplyed with a voltage, the output voltage changes when the oxygen concentration in the exhaust changes. This sensor, in comparison to the zirconiumdioxide sensor, requires no reference air. Due to this it is smaller in size.

Both sensors are a heated to quickly attain their operating temperature. During cold start, warm up and full throttle, lambda control is not in operation (open loop control). When lambda control operates, this is known as closed loop control.

Effects of failure

A faulty lambda sensor can produce the following effects:

  • High exhaust emission
  • Poor engine performance
  • High fuel consumption
  • Engine warning light illumination
  • Storing of a fault code

Causes of failure:

  • Internal and external short circuit
  • Missing supply voltage / ground
  • Overheating
  • Fouling / deposit build-up
  • Mechanical damage
  • Using leaded fuel / additive
  • Faulty heating element

Fault diagnosis

For the fault diagnosis consider the following steps:

  1. Visual inspection of the plug, plug contacts and wires for damage, correct fitting and routing
  2.  Read out the fault memory

Testing with an oscilloscope:

Connect the test cable of the oscilloscope to the lambda sensor. Consider the cable colours (observe the manufacturer¥s data):

  • –  Black: Signal wire
  • –  White: Signal ground wire
  • –  Grey: Heating element wire

Screen Shot 2017-04-20 at 14.50.06Adjustment of the X and Y axes Zirconiumdioxide sensor:

  • –  X axis (time): 5 seconds
  • –  Y axis (voltage): 2 volt
  • Warm up engine to operation temperature andhold 2000 rpm. On the oscilloscope a pattern is shown (see picture). There must be a minimum voltage of 0,1 V and maximum voltage of 0,9 V. The reaction time (riseing up from lean 0,1 V to rich 0,9 V) should be 300 milliseconds.

Adjustment of the X and Y axes Titaniumdioxide sensor:Screen Shot 2017-04-20 at 14.50.16

  • –  X axis (time): 10 seconds
  • –  Y axis (voltage): 5 volt

Warm up engine to operation temperature and hold 2000 rpm. On the oscilloscope a pattern is shown (see picture). There must be a minimum voltage of 0,2 V and maximum voltage of 4,5 V

Evaluation of the pattern:

The signal voltage of the sensors must be between 0,1V ñ 0,9 V for Zirconiumdioxide and 0,2 V ñ 4,4 V for Titaniumdioxide. If the signal voltage is out of this range the sensor is faulty. In this case, check the supply voltage of the titaniumdioxide sensor from the ECU ( note manufacturer data), before renewing the sensor. Also consider the switching duration ( frequency change between lean and rich) and the initial response time (reaction of a changed mixture). If the frequency is too low or the initial response time too long, the regulation is not optimal, the sensor should be renewed.

Screen Shot 2017-04-20 at 15.01.04As well as the electronic check and visual check of the connectors and wires, the condition of the protection sleeve of the sensor element can provide information about the operation.
The following statements apply to this:

  • The protection sleeve is heavily sooted (Fig. 1): Engine runs with a too rich mixture. The sensor should be renewed and the cause for the too rich mixture should be repaired to prevent a new sooting.
  • Bright deposits on the protective sleeve (Fig. 2): Use of leaded fuel. The lead destroys the sensor element. The sensor must be renewed and the catalytic converter must be checked. The leaded fuel must be changed to unleaded fuel.
  • Light (white or grey) deposit on the protective sleeve (Fig. 3): Engine burns oil, use of additional additive to the fuel. The sensor must be renewed and the cause of the oil burning must be rectified.
  • Improper installation (Fig.4): An improper installation can damage the sensor so that the optimal function can not be assured. Therefore, for fitting, the right special tool and the tightness should be observed.

Electrical exhaust gas recirculation valve Failure causes and troubleshooting

General information

EGR valves are installed in a bypass channel between the intake manifold and the exhaust manifold.
Recirculating part of the exhaust gas volume can reduce emissions of nitrogen oxides (NOx).

The EGR valve is activated by the engine control unit.

The exhaust gas recirculation rate is controlled depending on the engine speed, coolant temperature and engine load.Screen Shot 2017-04-12 at 14.42.20

Impact of failure

A failure of the exhaust gas recirculation may be noticed as follows:

  •   The engine control lamp turns on, error code is saved
  •   Black smoke (diesel)
  •   Rough idling
  •   Poor engine performance
  •   Jolting when accelerating Causes of failure

Causes of failure

Causes of failure may be:

  •   EGR valve blocked or constantly open
  •   Defective activation from control unit, grounding
  •   Defective, blocked lines
  •   Defective, blocked vacuum line
  •   Defective proportional valve
  •   Defective cables, poor contact at connections

Troubleshooting

The following points should be considered:
1. Checks using a diagnostic tool (if supported by system)

  •   Read out the keep alive memory
  •   Perform an actuating mechanism test
  •   Check system parameters (measured value blocks)

2. Visual inspection of all relevant components fordamage
3. Check the electrical wiring and connections fordamage, correct installation and good fit
4. Check the vacuum lines for leaks or blockages
5. Check the EGR valve and lines for blockage orcontamination
6. Check the voltage supply at the control unit andground connection at proportional valve, or directly at the EGR valve

Screen Shot 2017-04-12 at 14.44.22Example diagnostics

In the following, we would like to present the testing options on a removed exhaust gas recirculation valve.
The example we will use is the EGR valve from a Vauxhall Corsa C, model year 2002

Electrical test

The resistance between the contact pins in the valve connector is measured at room temperature using a multimeter. Please always observe the information provided by the vehicle manufacturer when performing these tests. Measurement:

1. connectors A and E = resistance 5.25 – 5.85 Ω 2. connectors B and D = resistance 2.10 – 4.90 kΩ 3. connectors B and C = resistance > 500 ΩScreen Shot 2017-04-12 at 14.45.21

Solenoid voltage test

Solenoid to a fused voltage supply, battery or power supply, connect with 12.0 to 13.5 volts.
Contact pin E to battery plus.
Cycle contact pin A to ground (max. 5x for 0.5 secs).

The valve must audibly operate and should open and fully close without disturbance.
Screen Shot 2017-04-12 at 14.48.59

Result

Although the electrical tests reveal no defects, it was clear to see that the valve is defective during the mechanical test. The valve pintle jams when open and cannot be moved by the tensile force of the solenoid.

Combustion residue deposits are the cause. As the vehicle grows older or in the event of a mechanical engine fault, the ingress of engine oil into the combustion chamber may intensify this contamination, potentially resulting in blockage of the valve (arrow). In this case, the cause should be remedied prior to replacing the EGR valve to prevent a further failure after a brief period.Screen Shot 2017-04-12 at 14.50.11

Comparison with a new EGR valve

As can clearly be seen in the image, the contaminated EGR valve (1) is already open in de-energized state.
The new valve closes perfectly at the pintle (2).Screen Shot 2017-04-12 at 14.50.33

Note

More information on exhaust gas recirculation can be found at:

www.hella.com/techworld

NOx sensors – background and function

Due to the need for reducing the delay in response time and the ever-improving accuracy of the control systems of the modern internal combustion engine, some new and very specific sensor technologies are being utilised by VMs. One critical area that has intense scrutiny is, of course, exhaust gas emissions.

Direct injection petrol engines, motorsport applications and even motorcycles place very specific demands on the technologies used for both exhaust gas measurement and its after-treatment, but it’s the DI engine that gives engineers a significant challenge in “keeping it clean” as you will learn as you read on.

Nitric oxide & nitrogen dioxide

In order to make petrol engines more economical and environmentally friendly, vehicle manufacturers are increasingly relying on direct petrol injection engines which can run at considerably leaner air/fuel mixtures under certain conditions, primarily partial load (cruise) conditions. The result of this can be an improvement of 12-20% in fuel consumption but, as with most things in life, there is a penalty to pay for this benefit.

One of the resultant gaseous compounds produced as a result of the combustion process within a spark ignition engine is what is known collectively as NOx. For the automotive industry this term is used to describe the nitric oxide and nitrogen dioxide contained within the exhaust gas. NOx compounds are environmentally damaging by-products of the combustion process and most vehicles deal effectively with this by the function of the three-way catalytic converter.

Spark ignition engines tend to produce greater quantities of these compounds when running at very lean fuelling conditions and the DI engine operates in this region when in stratified mode. The three-way catalyst cannot cope with this due to the excess oxygen contained within the exhaust gas which reforms the NOx, thus additional treatment of the exhaust gases is required.

NOx gas treatment

One counter-measure strategy is to use a NOx storage catalyst, an additional piece of hardware fitted onto the exhaust system, which temporarily stores and, at a predetermined point, chemically reduces the compounds to harmless nitrogen and oxygen. This function of “regeneration” is triggered by a change in the fuelling calibration, causing a temporary fuel rich state within the storage device.

A vital part of the control strategy for this system is the NOx sensor which is used to detect when the limit of storage capacity (saturation point) has been reached and then to instruct the fuelling management system to start the regeneration phase. The frequency of this cycle can be around once every 60 seconds and then the rich regeneration period commences for perhaps two seconds before reverting to lean mode.

The NOx sensor is an evolution of the wide band oxygen sensor and its element is constructed from special ceramics that contain two oxygen density detecting chambers that work together, allowing the determination of NOx concentration. Their function is quite complex and these sensors require dedicated ECUs which are either integrated into the vehicle’s control modules or may be contained within a unit permanently attached to the sensor harness.

It is common knowledge that most spark ignition vehicles must be fitted with a catalyst monitoring diagnostic sensor. However, this may not be the case where a NOx sensor is used.

The crucial role of NOx sensors

Due to the need for a reduction in response time delays and the ever increased accuracy of the control systems of the modern internal combustion engine, some new and very specific sensor technologies are being utilised by VMs. One critical area that is always under intense scrutiny is, of course, exhaust gas emissions.

Direct Petrol Injection

To make petrol engines more economical and environmentally friendly, VMs are increasingly relying on Direct Petrol Injection engines that can run at considerably leaner air/fuel mixtures under certain conditions – primarily partial load (cruise) conditions.

The result of this can be an improvement of 12-20% in fuel consumption, but, as with most things in life, there is a penalty to pay for this benefit.

One of the resultant gaseous compounds produced as a result of the combustion process within a spark ignition engine is known collectively as NOx. For the automotive industry, this term is used to describe the nitric oxide and nitrogen dioxide contained within the exhaust gas.

NOx compounds are environmentally damaging by-products of the combustion process, and most vehicles deal effectively with this by the use of a three-way catalytic converter. Spark ignition engines tend to produce greater quantities of these compounds when running at very lean fuelling conditions and the DI engine operates in this region when in ‘stratified’ mode.

The three-way catalyst can’t cope with this, due to the excess oxygen contained within the exhaust gas, which reforms the NOx; therefore, additional treatment of the exhaust gases is required.

Control strategy

One counter-measure strategy is to use a NOx storage catalyst – an additional piece of hardware fitted onto the exhaust system, which temporarily stores and, at a predetermined point, chemically reduces the compounds to harmless nitrogen and oxygen. This function of “regeneration” is triggered by a change in the fuelling calibration, causing a temporary fuel rich state within the storage device.

A vital part of the control strategy for this system is the NOx sensor, which is used to detect when the limit of storage capacity (saturation point) has been reached and will then instruct the fuelling management system to start the regeneration phase.

The frequency of this cycle can be around once every 60 seconds, then the rich regeneration period commences for around two seconds, before reverting to lean mode. The NOx sensor is an evolution of the wide band oxygen sensor and its element is constructed from special ceramics that contain two oxygen density detecting chambers that work together, allowing the determination of NOx concentration.

Their function is quite complex and these sensors require dedicated ECUs, which are either integrated into the vehicle’s control modules or are contained within a unit that is permanently attached to the sensor harness. It is common knowledge that most spark ignition vehicles must be fitted with a catalyst monitoring diagnostic sensor; however, this doesn’t have to be the case where a NOx sensor is used.